1. Field of the Invention
The present invention concerns an installation designed for demolition or destruction of constructions, such as buildings, industrial buildings, bridges, rock and in general, any natural structure or constructed structure (buildings, public works, underground works, quarries, etc.) wherein the demolition of destruction of the constructions is accomplished using explosives.
2. Discussion of Background
When constructions, bridges, materials, etc., are destroyed using explosives, a large number of small explosive charges are placed in holes drilled in the structures of the works to be demolished.
At the present time, these small charges are primed by medium or high intensity electrical detonators that are electrically fired by means of firing apparatus.
More precisely, in order to limit nuisances such as vibrations, blast, noise, etc., the global explosion is broken down into a multitude of small explosions which occur at specific time intervals.
Electric detonators with micro-delays are usually used for this purpose and are grouped in series (for example twenty units). A time interval (for example 25 thousandths of a second) is provided between each detonator in the same series.
Sequential type exploders are also usually used, in which several lines of detonators are fired at time intervals. Several sequential firing apparatuses may then be coupled.
When designed to demolish a residential building, existing installations operating according to the above stated principle comprise 1500 to 2000 detonators for each firing. Firing may last for 3 to 4 seconds, due to the spacing of explosion initiated by the installation. This firing takes place after preliminary work to install charges and primers which may last for 3 to 4 days, or even a week.
With current installations, accidental priming or failures may occur throughout the duration of the prior work to install charges and primers.
The main risk of accidental ignition is due to stray currents that may occur around primed charges. These stray currents may originate from a number of causes, such as lightning, currents originating from overhead or underground electrical networks, currents originating from nearby electrical installations in operation (electrical transformers, e.g., railway or tramway catenary lines, lights, etc.), and natural currents circulating underground when boring tunnels.
Charges may also be fired accidentally due to the use of electronic devices, such as radios, walkie-talkies, portable telephones, etc., in the vicinity of these charges.
Accidental firing of the detonators may also occur during transport or during storage, for example, due to stray currents or accidents of various types.
Since the drilling work may last for 3 or 4 days or even a week, there is also a risk that the previously installed charges may be fired mischievously by means of a simple electric battery.
Furthermore, when the construction to be demolished concerns the nuclear industry, as is particularly the case for demolition of a nuclear power station, existing demolition installations cannot be used at the time of firing due to disturbances that exist in an intense radioactive environment.
Existing electrically fired demolition installations are also affected by failures that can affect the demolition work. One particular cause of these failures is broken electric wires or wires in contact with metal structures, such as protective grills, metal equipment in buildings to be demolished, etc. When the construction to be demolished is a large metal structure, such as a thermal power station, failures may also be caused by electric fields produced by the enormous mass of steel in the building.
Furthermore, electric detonators used in existing demolition installations may be stolen and easily reused, both during their transport or storage, and after being installed in the construction to be demolished.
Finally, note that when there are any problems in the circuits of this type of demolition installation, these problems are frequently very long and dangerous to detect. It is easy to find out which line is defective, but it is impossible to know the exact location of the break in the circuit.